The high-power lithium-ion

Most lithium-ion batteries for portable applications are cobalt-based. The system consists of a cobalt oxide positive electrode (cathode) and a graphite carbon in the negative electrode (anode). One of the main advantages of the cobalt-based battery is its high energy density. Long run-time makes this chemistry attractive for cell phones, laptops and cameras.

The widely used cobalt-based lithium-ion has drawbacks; Toshiba PA3191U-1BRS Battery it offers a relatively low discharge current. A high load would overheat the pack and its safety would be jeopardized. The safety circuit of the cobalt-based battery is typically limited to a charge and discharge rate of about 1C. This means that a 2400mAh 18650 cell can only be charged and discharged with a maximum current of 2.4A. Another downside is the increase of the internal resistance that occurs with cycling and aging.Toshiba PA3166U-1BRS Battery, Toshiba PA3331U-1BRS Battery, Toshiba PA3098U-1BRS Battery, Toshiba PA3084U-1BRS Battery, After 2-3 years of use, the pack often becomes unserviceable due to a large voltage drop under load that is caused by high internal resistance. Figure 1 illustrates the crystalline structure of cobalt oxide.

Figure 1: Cathode crystalline of lithium cobalt oxide has 'layered' structures. The lithium ions are shown bound to the cobalt oxide. During discharge, the lithium ions move from the cathode to the anode. The flow reverses on charge.
In 1996, scientists succeeded in using lithium manganese oxide as a cathode material. This substance forms a three-dimensional spinel structure that improves the ion flow between the electrodes. High ion flow lowers the internal resistance and increases loading capability. The resistance stays low with cycling, however, the battery does age and the overall service life is similar to that of cobalt. Spinel has an inherently high thermal stability and needs less safety circuitry than a cobalt system.Low internal cell resistance is the key to high rate capability. This characteristic benefits fast-charging and high-current discharging. A spinel-based lithium-ion in an 18650 cell can be discharged at 20-30A with marginal heat build-up. Short one-second load pulses of twice the specified current are permissible. Some heat build-up cannot be prevented and the cell temperature should not exceed 80°C.
Figure 2: Cathode crystalline of
lithium manganese oxide has a
'three-dimensional framework structure'.
This spinel structure, which is usually composed of diamond shapes connected into a lattice,Toshiba PA3166U-1BRS Battery appears after initial formation. This system provides high conductivity but lower energy density.

The spinel battery also has weaknesses. One of the most significant drawbacks is the lower capacity compared to the cobalt-based system. Spinel provides roughly 1200mAh in an 18650 package, about half that of the cobalt equivalent. In spite of this,Toshiba PA3166U-1BRS Battery, Toshiba PA3331U-1BRS Battery, Toshiba PA3098U-1BRS Battery, Toshiba PA3084U-1BRS Battery, spinel still provides an energy density that is about 50% higher than that of a nickel-based equivalent. Figure 3: Format of 18650 cell.
The dimensionsof this commonly used cell are: 18mm in diameter and 65mm in length.

Types of lithium-ion batteries
Lithium-ion has not yet reached full maturity and the technology is continually improving. The anode in today's cells is made up of a graphite mixture and the cathode is a combination of lithium and other choice metals. It should be noted that all materials in a battery have a theoretical energy density. With lithium-ion, the anode is well optimized and little improvements can be gained in terms of design changes. The cathode, however, shows promise for further enhancements. Battery research is therefore focusing on the cathode material. Another part that has potential is the electrolyte. The electrolyte serves as a reaction medium between the anode and the cathode.

The battery industry is making incremental capacity gains of 8-10% per year. This trend is expected to continue. This, however, is a far cry from Moore's Law that specifies a doubling of transistors on a chip every 18 to 24 months. Translating this increase to a battery would mean a doubling of capacity every two years. Instead of two years, lithium-ion has doubled its energy capacity in 10 years.
Today's lithium-ion comes in many "flavours" and the differences in the composition are mostly related to the cathode material. Table 1 below summarizes the most commonly used lithium-ion on the market today. For simplicity,Toshiba PA3098U-1BRS Battery we summarize the chemistries into four groupings, which are Cobalt, Manganese, NCM and Phosphate.

Table 1: Most common types of lithium-ion batteries.

The cobalt-based lithium-ion appeared first in 1991, introduced by Sony. This battery chemistry gained quick acceptance because of its high energy density. Possibly due to lower energy density, spinel-based lithium-ion had a slower start. When introduced in 1996, the world demanded longer runtime above anything else. With the need for high current rate on many portable devices, spinel has now moved to the frontline and is in hot demand. The requirements are so great that manufacturers producing these batteries are unable to meet the demand. This is one of the reasons why so little advertising is done to promote this product. E-One Moli Energy (Canada) is a leading manufacturer of the spinel lithium-ion in cylindrical form. They are specializing in the 18650 and 26700 cell formats.Toshiba PA3166U-1BRS Battery, Toshiba PA3331U-1BRS Battery, Toshiba PA3098U-1BRS Battery, Toshiba PA3084U-1BRS Battery, Other major players of spinel-based lithium-ion are Sanyo, Panasonic and Sony.

Sony is focusing on the nickel-cobalt manganese (NCM) version. The cathode incorporates cobalt, nickel and manganese in the crystal structure that forms a multi-metal oxide material to which lithium is added. The manufacturer offers a range of different products within this battery family, Toshiba PA3084U-1BRS Battery catering to users that either needs high energy density or high load capability. It should be noted that these two attributes could not be combined in one and the same package; there is a compromise between the two. Note that the NCM charges to 4.10V/cell, 100mV lower than cobalt and spinel. Charging this battery chemistry to 4.20V/cell would provide higher capacities but the cycle life would be cut short. Instead of the customary 800 cycles achieved in a laboratory environment, the cycle count would be reduced to about 300.